Longitudinal shear loading of a unidirectional composite.
Fiber reinforced composite material behavior examined from shear loading tests, using finite difference analysis for representative PDEs
FIBER STRENGTH↗
SEARCH · Engineering Papers
Results for “differential strain”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Creep response of the lunar crust in mare regions from an analysis of crater deformation
The settling trends of 318 lunar mare craters are compared with predictions of numerical finite-element models in order to determine the creep response of the upper lunar mare crust. No settling is evident in craters smaller than 5 km in diameter. Settling rates of larger craters increase as function of crater size in a manner suggesting a nonlinear lunar creep response corresponding to the power law epsilon = 8.3 x 10 to the minus 34th sigma squared where epsilon is the strain rate and sigma is the differential stress. However, the observed nonlinearity is probably an apparent nonlinearity resulting from the temperature-induced viscosity decrease with depth due to a lunar crustal temperature gradient of 3 C/km and a creep activation energy of 20 kcal/mole. It is concluded that creep in the lunar medium is essentially Newtonian, and that the effective viscosity of the upper lunar mare is (1.6 plus or minus 0.3) x 10 to the 25th poise.
Kunze, A. W. G.↗
Experiments on Diffusion Flame Structure of a Laminar Vortex Ring
The study of flame-vortex interactions provides one of the means to better understand turbulent combustion, and allows for canonical configurations that contain the fundamental elements found in turbulent flames, These include concentrated vorticity, entrainment and mixing, strain and nonequilibrium phenomena, diffusion and differential diffusion, partial premixing and diluent effects, and heat release effects. In flame- vortex configurations, these fundamental elements can be studied under more controlled conditions than is possible in direct investigations of turbulent flames. Since the paper of Marble, the problem of the flame-vortex interaction has received considerable attention theoretically, numerically and experimentally. Several configurations exist for study of the premixed flame/vortex ring interaction but more limited results have been obtained to date for the diffusion flame/vortex ring case. The setup of Chen and Dahm, which is conceptually similar to that of Karagozian and Manda and Karagozian, Suganuma and Strom where the ring is composed of fuel and air and combustion begins during the ring formation process, is used in the current study. However, it is essential to conduct the experiments in microgravity to remove the asymmetries caused by buoyancy and thus obtain highly symmetric and repeatable interactions. In previous studies it was found that the flame structure of the vortex ring was similar to that obtained analytically by Karagozian and Manda. Dilution of propane with nitrogen led mainly to a reduction in flame luminosities, flame burnout times were affected by both fuel volumes and amount of dilution, and a simple model of the burnout times was developed. In this paper, a discussion on reacting ring displacement and flame burnout time will be given, and the flame structures of vortex rings containing ethane and air will be compared to those of propane reacting in air.
Chen, Shin-Juh↗
Turbulent Flame Processes Via Diffusion Flame-Vortex Ring Interactions
Flame-vortex interactions are canonical configurations that can be used to study the underlying processes occurring in turbulent reacting flows. This configuration contains many of the fundamental aspects of the coupling between fluid dynamics and combustion that could be investigated with more controllable conditions than are possible under direct investigations of turbulent flames. Diffusion flame-vortex ring interaction contains many of the fundamental elements of flow, transport, combustion, and soot processes found in turbulent diffusion flames. Some of these elements include concentrated vorticity, entrainment and mixing, strain and nonequilibrium phenomena, diffusion and differential diffusion, partial premixing and diluent effects, soot formation and oxidation, and heat release effects. Such simplified flowfield allows the complex processes to be examined more closely and yet preserving the physical processes present in turbulent reacting flows. Furthermore, experimental results from the study of flame-vortex interactions are useful for the validation of numerical simulations and more importantly to deepen our understanding of the fundamental processes present in reacting flows. Experimental and numerical results obtained under microgravity conditions of the diffusion flame-vortex ring interaction are summarized in this paper. Results are obtained using techniques that include Flame Luminosity Imaging (FLI), Laser Soot-Mie Scattering (LSMS), Computational Fluid Dynamics and Combustion (CFDC), and Diode Laser Spectroscopy/Iterative Temperature with Assumed Chemistry (DLS/ITAC).
Dahm, Werner J. A.↗
Spatiotemporal features of early neuronogenesis differ in wild-type and albino mouse retina
In albino mammals, lack of pigment in the retinal pigment epithelium is associated with retinal defects, including poor visual acuity from a photoreceptor deficit in the central retina and poor depth perception from a decrease in ipsilaterally projecting retinal fibers. Possible contributors to these abnormalities are reported delays in neuronogenesis (Ilia and Jeffery, 1996) and retinal maturation (Webster and Rowe, 1991). To further determine possible perturbations in neuronogenesis and/or differentiation, we used cell-specific markers and refined birth dating methods to examine these events during retinal ganglion cell (RGC) genesis in albino and pigmented mice from embryonic day 11 (E11) to E18. Our data indicate that relative to pigmented mice, more ganglion cells are born in the early stages of neuronogenesis in the albino retina, although the initiation of RGC genesis in the albino is unchanged. The cellular organization of the albino retina is perturbed as early as E12. In addition, cell cycle kinetics and output along the nasotemporal axis differ in retinas of albino and pigmented mice, both absolutely, with the temporal aspect of the retina expanded in albino, and relative to the position of the optic nerve head. Finally, blocking melanin synthesis in pigmented eyecups in culture leads to an increase in RGC differentiation, consistent with a role for melanin formation in regulating RGC neuronogenesis. These results point to spatiotemporal defects in neuronal production in the albino retina, which could perturb expression of genes that specify cell fate, number, and/or projection phenotype.
NASA Discipline Developmental Biology↗
Modeling creep behavior of fiber composites
A micromechanical model for the creep behavior of fiber composites is developed based on a typical cell consisting of a fiber and the surrounding matrix. The fiber is assumed to be linearly elastic and the matrix nonlinearly viscous. The creep strain rate in the matrix is assumed to be a function of stress. The nominal stress-strain relations are derived in the form of differential equations which are solved numerically for off-axis specimens under uniaxial loading. A potential function and the associated effective stress and effective creep strain rates are introduced to simplify the orthotropic relations.
Chen, J. L.↗
Measurement of residual strains in boron-epoxy and glass-epoxy laminates
Embedded-strain-gage techniques were developed and used for measuring strains in composite angle-ply laminates during curing and thermal cycling. The specimens were 2.54 by 22.9 cm eight-ply boron-epoxy and S-glass-epoxy laminates. Unidirectional specimens were used for control purposes. Strain readings were corrected for the purely thermal output of the gages obtained from an instrument quartz reference specimen. The strains measured during the cooling part of the curing cycle were in agreement with those recorded during subsequent thermal cycling, indicating that residual stresses induced during curing are primarily caused by differential thermal expansions of the various plies. Restraint strains were computed for the 0-deg and 45-deg plies of the angle-ply laminates tested, and the residual stresses obtained using the anisotropic constitutive relations and taking into account the temperature dependence of stiffnesses and strains.
Daniel, I. M.↗
PLZT block data composers operated in differential phase mode
The use of a PLTZ block data composer as a matrix type phase modulator to record and process digital data by the differential phase mode in a holographic recording/processing system was investigated. The system has readout contrast ratios of between 10 and 15 to 1. The differential phase mode has the advantage that strain bias is not required and thickness and strain variations in the PLZT are cancelled out.
Drake, M. D.↗
Solder Creep-Fatigue Interactions with Flexible Leaded Part
In most electronic packaging applications it is not a single high stress event that breaks a component solder joint; rather it is repeated or prolonged load applications that result in fatigue or creep failure of the solder. The principal strain in solder joints is caused by differential expansion between the part and its mounting environment due to hanges in temperature (thermal cycles) and/or due to temperature gradients between the part and the board.
creep effects↗
Differential expansion fitting for cryogenic liquid tanks
Sliding contact between liner and interior surface of fitting accommodates stresses and strains developed in shell composite and metal liner system. Stresses and strains are transmitted to liner portion which is recessed in fitting and which acts as differential expansion fitting.
Landes, R. E.↗
PLZT block data composers operated in differential phase mode
The use of PLZT ceramics with the 7/65/35 composition in block data composer (BDC) input devices for holographic memory systems has previously been described for operation in the strain biased, scattering, and edge effect modes. A new and promising mode of BDC operation is the differential phase mode in which each element of a matrix array BDC acts as a phase modulator. The phase modulation results from a phase difference in the optical path length between the electrically poled and depoled states of the PLZT. It is shown that a PLZT BDC can be used as a matrix-type phase modulator to record and process digital data by the differential phase mode in a holographic recording/processing system with readout contrast ratios of between 10:1 and 15:1. The differential phase mode has the advantages that strain bias is not required and that the thickness and strain variations in the PLZT are cancelled out.
Drake, M. D.↗
Influence of reforming processes on the fracture strength of solids.
Reformation processes effect on stress-time-to- fracture behavior of solids, considering governing differential equation
FRACTURE TOUGHNESS↗
Calibratable pressure switch /solid state/ Final report
Differential pressure switch based on photosensitive semiconductor and strain gages
Brown, S. H.↗
On numerical nonlinear analysis of highly flexible spinning cantilevers
The general nonlinear discretized equations of motion of spinning elastic solids and structures are derived as a set of nonlinear ordinary differential equations for the case when the strain-displacement and velocity-displacement relations are nonlinear up to the second order. It is shown that the cost of generation of such equations is proportional to the fourth power of the number of degrees of freedom. A computer program is written to automatically generate the equations for the case of spinning cantilevers with initial imperfections. The types and the number of the coordinate functions used in the trial solution are parameters of the program.
Utku, S.↗
Experimental verification of damping mechanisms in a composite beam
A method of estimating the distributed damping parameters based on the measured modal parameters (frequency and damping ratios) was derived. Three different mathematical models were used to model the damping mechanism of a quasi-isotropic pultruded cantilevered beam. These three models were (1) viscous (air) damping, (2) strain rate damping, and (3) both viscous and strain rate damping. The eigenvalues of the partial differential equation model were found to be uninfluenced by any of the three assumed damping models. Values were obtained for each of the damping models as well as the modulus of elasticity of the beam. It was found that the two-parameter damping model provided the best fit to measured modal data. However, the two-parameter damping model could only reproduce the measured damping ratios to within 85 percent.
Cudney, Harley H.↗
Payload Hardware and Experimental Protocol for Testing the Effect of Space Microgravity on the Resistance to Gentamicin of Stationary-Phase Uropathogenic Escherichia Coli and Its Sigma (sup S)-Deficient Mutant
Human immune response is compromised and bacteria can become more antibiotic resistant in space microgravity (MG). We report that under low-shear modeled microgravity (LSMMG) stationary-phase uropathogenic Escherichia coli (UPEC) become more resistant to gentamicin (Gm). UPEC causes urinary tract infections (UTIs), reported to afflict astronauts; Gm is a standard treatment, so these findings could impact astronaut health. Because LSMMG has been shown to differ from MG, we report here preparations to examine UPEC's Gm sensitivity during spaceflight using the E. coli Anti-Microbial Satellite (EcAMSat) on a free flying nanosatellite in low Earth orbit. Within EcAMSats payload, a 48-microwell fluidic card contains and supports study of bacterial cultures at constant temperature; optical absorbance changes in cell suspensions are made at three wavelengths for each microwell and a fluid-delivery system provides growth medium and predefined Gm concentrations. Performance characterization is reported for spaceflight prototypes of this payload system. Using conventional microtiter plates, we show that Alamar Blue (AB) absorbance changes due to cellular metabolism accurately reflect E. coli viability changes: measuring AB absorbance onboard EcAMSat will enable telemetry of spaceflight data to Earth. Laboratory results using payload prototypes are consistent with wellplate and flask findings of differential sensitivity of UPEC and its delta rpoS strain to Gm. Space MG studies using EcAMSat should clarify inconsistencies from previous space experiments on bacterial antibiotic sensitivity. Further, if sigma (sup s) plays the same role in space MG as in LSMMG and Earth gravity, EcAMSat results would facilitate utilizing our previously developed terrestrial UTI countermeasures in astronauts.
Matin, A. C.↗
A computer program for the geometrically nonlinear static and dynamic analysis of arbitrarily loaded shells of revolution, theory and users manual
A digital computer program known as SATANS (static and transient analysis, nonlinear, shells) for the geometrically nonlinear static and dynamic response of arbitrarily loaded shells of revolution is presented. Instructions for the preparation of the input data cards and other information necessary for the operation of the program are described in detail and two sample problems are included. The governing partial differential equations are based upon Sanders' nonlinear thin shell theory for the conditions of small strains and moderately small rotations. The governing equations are reduced to uncoupled sets of four linear, second order, partial differential equations in the meridional and time coordinates by expanding the dependent variables in a Fourier sine or cosine series in the circumferential coordinate and treating the nonlinear modal coupling terms as pseudo loads. The derivatives with respect to the meridional coordinate are approximated by central finite differences, and the displacement accelerations are approximated by the implicit Houbolt backward difference scheme with a constant time interval. The boundaries of the shell may be closed, free, fixed, or elastically restrained. The program is coded in the FORTRAN 4 language and is dimensioned to allow a maximum of 10 arbitrary Fourier harmonics and a maximum product of the total number of meridional stations and the total number of Fourier harmonics of 200. The program requires 155,000 bytes of core storage.
Ball, R. E.↗
Design of an Auto-zeroed, Differential, Organic Thin-film Field-effect Transistor Amplifier for Sensor Applications
Organic strain gauge and other sensors require high-gain, precision dc amplification to process their low-level output signals. Ideally, amplifiers would be fabricated using organic thin-film field-effect transistors (OTFT's) adjacent to the sensors. However, OTFT amplifiers exhibit low gain and high input-referred dc offsets that must be effectively managed. This paper presents a four-stage, cascaded differential OTFT amplifier utilizing switched capacitor auto-zeroing. Each stage provides a nominal voltage gain of four through a differential pair driving low-impedance active loads, which provide common-mode output voltage control. p-type pentacence OTFT's are used for the amplifier devices and auto-zero switches. Simulations indicate the amplifier provides a nominal voltage gain of 280 V/V and effectively amplifies a 1-mV dc signal in the presence of 500-mV amplifier input-referred dc offset voltages. Future work could include the addition of digital gain calibration and offset correction of residual offsets associated with charge injection imbalance in the differential circuits.
large-area electronics↗